The ink-jet recording has such a lot of advantages that a high-speed recording is possible; a low noise level is achieved; colorization is easy; a high resolution can be made; and a plain paper recording is possible. Because of these advantages, instruments and equipments using such recording method are remarkably in widespread use. As the ink used in this recording method, an aqueous ink is dominant from the viewpoints of safety, odor and the like. In the ink-jet recording method, image formation is performed by ejecting (discharging) the ink in a rate of several thousands or more drops per second.
In the case where a high-speed printing is performed by the ink-jet recording method, aggregation and color bleeding may occur. Specifically, the term “aggregation” signifies a phenomenon in which before absorption of the first ink droplet into a paper has been completed, the second ink droplet reaches to the first ink droplet and they are united or aggregated to form one large liquid droplet. The image resolution is deteriorated by the aggregation. On the other hand, the term “color bleeding” signifies a phenomenon in which image sharpness and color quality are deteriorated on the grounds that two droplets, which are to be united, contain a colorant having a different color from each other.
As a method contemplated to address the problem of color bleeding in a high-speed printing, a method of using an ink that turns into a gel in response to heat, and printing the ink on a recording element (paper) having been heated at a higher temperature than that of the ink is proposed (see JP-A-2003-285532 (“JP-A” means unexamined published Japanese patent application)).
Other than the color bleeding, various kinds of properties such that clogging in a recording apparatus is not caused; intermittent ejection stability is secured; and the like are demanded for the ink jet ink. One example of the inks by which such properties have been improved is an ink containing urea, which is described in JP-A-8-120204.
In the mean time, improvement of bleeding and suppression of penetration of the ink through the paper (transfer of the ink to the back side of the paper) have been further strongly required for the ink-jet recording pigment ink. The present inventors have confirmed that although the color bleeding is improved by a technique described in JP-A-2003-285532, the effect of improvement is not enough. Further, sometimes, a density on the printing side becomes low due to penetration of the ink through the paper whereby it becomes difficult to obtain a necessary optical density (OD). In addition, improvement of ejectability (ejection property), especially improvement relating to a delay of ejection is desired. Further, the printing method described in JP-A-2003-285532 needs to heat a recording element; and in Examples thereof, printing is carried out by heating to 85° C. Therefore, it is also desired to lower the heating temperature thereby reducing the load on a recording apparatus or a recording system as well as energy consumption.